1. Field of the Invention
Embodiments of the present invention relate to an organic light emitting device and a method for manufacturing the same, which can reduce the manufacturing cost as well as thickness and weight of the device.
2. Discussion of the Related Art
A liquid crystal display device has been widely used as a flat panel display device. However, the liquid crystal display device requires a back light as a separate light source and has also technical limitations in brightness, contrast ratio, and viewing angle.
Recently, an organic light emitting device, which does not require a separate light source due to its self light-emission and has relatively excellent brightness, contrast ratio and viewing angle, has received much attention.
This organic light emitting device may be divided into a passive matrix type organic light emitting device and an active matrix type light emitting device in accordance with a driving mode.
In the passive matrix type organic light emitting device, a thin film transistor (TFT) is not separately provided and pixels are arranged in a matrix arrangement. Also, since each pixel is driven by sequential driving of scanning lines, higher voltage and higher current should instantaneously be applied to the passive matrix type organic light emitting device as the scanning lines are increased. Accordingly, power consumption is increased and there is limitation in resolution.
On the other hand, in the active matrix type light emitting device, a TFT is formed at each of pixels arranged in a matrix arrangement. Also, each pixel is driven by switching driving of the TFT and voltage charging of a storage capacitor Cst.
The active matrix type light emitting device is advantageous in that it has lower power consumption and higher resolution than the passive matrix type light emitting device. Accordingly, the active matrix type light emitting device is suitable for a display device that requires high resolution and a large display area.
Hereinafter, an active matrix type organic light emitting device according to a related art will be described with reference to the accompanying drawings. In this specification, the active matrix type organic light-emitting device will briefly be referred to as an organic light emitting device.
FIG. 1 is a cross-sectional view illustrating a frit sealing type organic light emitting device according to the related art.
A light emitting region of an entire region of the organic light emitting device is only shown in FIG. 1. In FIG. 1, a TFT array region where a switching TFT and a driving TFT for driving an organic light emitting diode (OLED) 20 are formed is not shown.
Referring to FIG. 1, the organic light emitting device according to the related art includes a glass substrate 10, which is a base substrate, an OLED 20 emitting light depending on a current input by driving of the switching TFT and the driving TFT, a frit 30 protecting the OLED 20, and a sealing glass (or encap glass) 40 for sealing pixels.
In this case, the frit 30 includes a glass powder for protecting the OLED 20 from an external factor such as moisture.
The glass substrate 10 may be made of a transparent glass having a plate shape, and may be formed using a material such as potassium lime, soda lime or quartz.
Although not shown, the organic light emitting device according to the related art may further include a polarizing layer for polarizing light from the OLED 20, a cover glass arranged on a display panel, and an adhesive layer for attaching the cover glass to the display panel.
FIG. 2 is a brief diagram illustrating a light emitting structure of the OLED according to the related art.
Referring to FIG. 2, the OLED 20 is a transparent electrode on the glass substrate 10, and is provided with an anode electrode 21 used as a positive electrode.
A hole injection layer 22, a light emitting layer 23 and an electron injection layer 24 are sequentially deposited on the anode electrode 21. A cathode electrode 25 used as a negative electrode is formed on the electron injection layer 24.
If electrons generated by the cathode electrode 25 and holes generated by the anode electrode 21 are injected into the light emitting layer 23, the electrons and holes are combined with one another to generate excitons. When the generated excitons are shifted from an exited state to a ground state, light is emitted, whereby picture images are displayed.
FIG. 3 is a cross-sectional view illustrating a front sealing type organic light emitting device according to the related art.
Referring to FIG. 3, the front sealing type organic light emitting device according to the related art includes a glass substrate 10, which is a base substrate, an OLED 20 emitting light depending on a current input by driving of a switching TFT and a driving TFT, a passivation layer 50 formed to cover the OLED 20, an adhesive layer 60 formed to cover the passivation layer 50, and a sealing glass (or encap glass) 40 formed on the adhesive layer 60 to seal the OLED 20.
The passivation layer 50 is to protect the OLED 20 from an external factor such as moisture, and is formed to cover the OLED 20. The adhesive layer 60 is formed on the passivation layer 50, and the sealing glass 40 is formed on the adhesive layer 60.
The sealing type organic light emitting device according to the related art planarizes the glass substrate 10 through the adhesive layer 60. The sealing glass 40 is attached onto the adhesive layer 60 to seal the OLED 20 from the external factor such as moisture.
The organic light emitting device according to the related art, which has the aforementioned structures of FIG. 1 and FIG. 3, is manufactured by sequentially performing the steps of forming a TFT in an array region, manufacturing the OLED by depositing an organic material, and sealing the light emitting region.
However, the OLED 20 of the related art, which should be sealed from the outside due to its vulnerability to moisture, has problems as follows.
Since the frit sealing type organic light emitting device according to the related art shown in FIG. 1 seals the OLED 20 from the external factor such as moisture by using the glass powder, the frit 30 and the sealing glass 40 are used.
Also, the front sealing type organic light emitting device according to the related art shown in FIG. 3 seals the OLED 20 from the external factor such as moisture by forming the passivation layer 50 and the adhesive layer 60 on the OLED 20 and forming the sealing glass 40.
In this case, as the sealing glass 40 is formed on the OLED 20, a problem occurs in that the thickness is increased. A problem also occurs in that the manufacturing cost is increased as the sealing glass 40 is used.